I found Nate Silver's piece on prospect rankings very interesting and thought others may wish to take a look. This is an open article, and does not require a subscription...

http://www.baseballprospectus.com/article.php?articleid=4750

I think I have always had the view expounded here regarding prospect rankings.  

Of course this is also why I like John's approach. He has a general system he tries to follow. So players in A ball are viewed a little more skeptically, often because their projections are similar to what older players in AAA are currently doing. I appreciate the objectivity. (Although I generally adjust John's grades downward some for when he ranks AL Central prospects - I've felt Detroit, Minnesota and KC tend to be the Lucy to John's Charlie Brown on many occasions...=)